<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="utf-8">
    <title>title</title>
    <style>
        div {
            width: 1100px;
            height: 300px;
            background-color: skyblue;
            margin: 0px auto;
        }
        
        li {
            float: left;
            list-style: none;
            background-color: springgreen;
            width: 300px;
            height: 300px;
            margin-right: 100px;
            line-height: 300px;
            text-align: center;
        }
        
        .last {
            margin-right: 0px;
        }
    </style>
</head>

<body>
    <div>
        <li>盒子1</li>
        <li>盒子2</li>
        <li class="last">盒子4</li>
    </div>
</body>

</html>